as you've suggested, early humans surely worked hard, used their brains to come up with new, workable ideas, and prospered as a result. That many died out or were wiped out is a normal expectation for young civilizations that encountered overwhelming odds. Perhaps a few survived and shared their knowledge with others or maybe they didn't and every group had to start from scratch? Who knows? What is clear is that some humans survived, evolved, mixed, and we are the result.